Whenever I want to check an already opened page (when switching between tabs or applications), Internet Explorer reloads the page. As a consequence, I can't keep opened pages without internet access. Is there a way to prevent this ?
Tabs that you've used stay in memory as long as Internet Explorer stays in memory (i.e. it shows in the list when pressing, and holding the back button). If the Internet Explorer falls off the list of running applications, the open tabs are preserved, but are refreshed the next time you use them - this is the same behaviour as the desktop version (and, for that matter, for competitor browsers, such as Firefox on the desktop)
Why it reloads the page. For once see it from Mobile's point of view.
Why purge previous page : If it is not having to reload the page then it has to hold the page data somewhere into memory and keep a pointer/object busy into stack. Meaningfully more memory will be used and phone will be prone to hanged. To avoid such a tragedy that your window's phone getting hanged/freeze Microsoft has not allowed this. This is an advantage.
Alternative solution : You can use Mozilla's firefox web browser in your windows phone. This browser keep the hold of previous loaded page. It will suite your need but still might get hanged. Hope you understand the compromise on memory.
Windows phone are famous for their UX(user experience) UI(design etc) fast and fluid experience.